Many applications exist for seals, gaskets, flexible supports and the like having soft rubber or rubber-like elastomer bonded to a metal substrate. For example, in the Space Shuttle program exhaust nozzles of solid-fuel rocket motors utilize flex seals of plasticized elastomer bonded to surfaces of the nozzles. A strong, high-quality bond is required to withstand the severe environments to which such seals are subjected in their operating life. Bonding of elastomer to the metal surface for this purpose has been carried out by cleaning the metal surface, applying a primer and an adhesive and pressing the elastomer to the adhesive while heating at 300.degree. F. for one hour. The bond obtained by such procedure frequently has failed under pressure or other loads owing to weakness resulting from diffusion of plasticizing agents into the adhesive layer during bonding.
Various prior patents disclose bonding processes in which a thin film of rubber or rubber-like material is interposed between a metal surface and a rubber article being joined to the surface. U.S. Pat. No. 1,732,886 discloses application of a film of tacky, thermoplastic rubber isomers to the metal, heating the film and vulcanizing a rubber composition in contact with the film. In U.S. Pat. No. 1,749,824 after a layer of cement is applied to the metal, a series of layers containing a mixture of cement and rubber is applied, each successive layer being made up to contain more rubber and less cement. The rubber article is then bonded to the last, rubber-rich layer. U.S. Pat. No. 2,144,495 discloses use of an intermediate film of synthetic drying oils mixed with rubber stock in solution. The film is applied, and rubber is bonded thereto by means of a second coating that adheres both to the film and the rubber. None of these patents is concerned with soft rubber in the form of modern-day plasticized elastomers or with prevention of diffusion of plasticizers into an adhesive bonded joint.